1. Field of the Invention
The present invention relates generally to a communication apparatus and method in a broadband wireless communication system, and in particular, to an apparatus and method for setting a guard band with respect to an asynchronous Base Station (BS) in a broadband wireless communication system.
2. Description of the Related Art
A number of radio communication technologies have been suggested as a candidate for rapid mobile communications. Among the suggested technologies, an Orthogonal Frequency Division Multiplexing (OFDM) scheme is the most dominant next-generation radio communication technology. In the future, it is anticipated that the OFDM technology will be adopted by most of the radio communication technologies. Wireless Metropolitan Area Network (WMAN) of Institute of Electrical and Electronics Engineers (IEEE) 802.16, which is called the 3.5G technology, is adopting the OFDM technology as the standard.
Since interference caused by asynchronization in the radio communication system may affect not only its own system but also other systems in general, time synchronization is quite important in the system operation. In response to this, various techniques have been suggested to acquire the synchronization between the BSs in the existing network. However, with respect to time offset in the network, there is no specific solution for addressing the performance degradation of the Mobile Station (MS) and the time offset.
When synchronization between the BSs is deprived in the synchronous network, the time offset is compensated over a wired or wireless network. In this case, the MS is subject to the interference increase and thus its Quality of Service (QoS) is not ensured.
FIG. 1 is a graph of an interference power of a conventional MS allocated a specific band from its neighbor bands.
In FIG. 1, when the specific band is allotted to the MS, the interference of the outer subcarriers is greater than the interference of the inner subcarriers. The influence of the interference results from the most adjacent subcarriers. Also, the greater time offset, the greater interference.
When the time offset occurs owing to a clock drift in the synchronous network, the MSs in the cell boundary cannot receive signals because of the interference from a neighbor BS (or a neighbor band). Also, when a new BS is plugged, the MSs cannot receive signals because of the time offset with the neighbor BS.
Accordingly, there is a need for a method of guaranteeing the QoS of the MS when there occurs the time offset owing to the clock drift or the newly plugged BS.